This design constitutes a self-resetting
(gain quenching), room-temperature
operational semiconductor single-photon-sensitive detector that is sensitive to
telecommunications optical wavelengths
and is scalable to large areas
(millimeter diameter) with high bandwidth
and efficiencies.

The device can detect single photons
at a 1,550-nm wavelength at a gain of 1 ×
106. Unlike conventional single photon
avalanche detectors (SPADs), where
gain is an extremely sensitive function to
the bias voltage, the multiplication gain
of this device is stable at 1 × 106 over a
wide range of bias from 30.2 to 30.9 V.
Here, the multiplication gain is defined
as the total number of charge carriers
contained in one output pulse that is
triggered by the absorption of a single
photon. The statistics of magnitude of
output signals also shows that the device
has a very narrow pulse height distribution,
which demonstrates a greatly suppressed
gain fluctuation. From the histograms
of both pulse height and pulse
charge, the equivalent gain variance
(excess noise) is between 1.001 and
1.007 at a gain of 1 × 106. With these
advantages, the device holds promise function
as a PMT-like photon counter
at a 1,550-nm wavelength.

The epitaxial layer structure of the
device allows photons to be absorbed in
the InGaAs layer, generating electron/
hole (e-h) pairs. Driven by an electrical
field in InGaAs, electrons are collected
at the anode while holes reach the multiplication
region (InAlAs p-i-n structure)
and trigger the avalanche process.
As a result, a large number of e-h pairs
are created, and the holes move toward
the cathode. Holes created by the avalanche
process gain large kinetic energy
through the electric field, and are considered
“hot”. These hot holes are
cooled as they travel across a p-InAlAs
low field region, and are eventually
blocked by energy barriers formed by
the InGaAsP/InAlAs heterojunctions.

The composition of the InGaAsP alloy
was chosen to have an 80 meV valance
band offset with InAlAs, which is high
enough to hinder the transport of the
already cooled holes. Being stopped by
the energy barrier, holes are accumulated
at the junctions to shield the electric field,
resulting in a decrease of the electric field
in the multiplication region. Because the
impact ionization rate is extremely sensitive
to the magnitude of the electric field,
the field-screening effect drastically
reduces the impact ionization rate and
quenches the output signals.

After the avalanche pulse signal is self-quenched,
the accumulated holes at the
InGaAsP/InAlAs interface escape the
energy barrier through thermal excitation
and tunneling and finally leave the device.
The device is thus reset and ready for subsequent
photon detection. This recovery
time is controlled by the height of the
energy barrier and the hole-cooling rate.

This work was done by Kai Zhao and Yu-Hwa Lo of the University of California San
Diego and William Farr of Caltech for
NASA’s Jet Propulsion Laboratory. For
more information, download the Technical
Support Package (free white paper) at
www.techbriefs.com/tsp under the Physical
Sciences category. NPO-45801

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